Got to disagree wit you on this QRN
Horizontal is likely best for DX
better low angle (typically)
also goes further(typically) before being refracted on first hop
Circular on the other hand
is more resistant to fade
and therefore is easier for other party to listen longer to one who is talking circular
Advantages to both
but Horizontal wins out
Except if both the receiving and transmitting signal is circular
only then does circular win out
because most people use either vertical or horizontal
circular losses 1.5 Db typically to the listening station
(not always very bad thing though)